Automated Dot Mapping: How to Dot the Dot Map

Abstract

Dot mapping is a cartographic representation method to visualize quantitative absolute values, e.g. population figures, and spatial distribution patterns. In the course of the development of computer-assisted cartography many cartographic methods have already been implemented in computer algorithms, but for dot mapping only a few solutions with some considerable constraints have been found until now. The most important constraint is the lack of repeatable results because these solutions work with random dot placement. This may result in different maps, where the only real difference is the date of production, not the data that is mapped. Another constraint is the overlap of dots which may interfere with the user's intention to count the dots. Although, this last constraint may not be considered important by all, the first constraint is clearly problematic for the cartographer. This paper deals with the automated production of dot distribution maps which will not suffer from the above named constraints. The paper focuses on the placement of dots. It presents a method of placing dots in a centred manner as dot clusters grouping around one central point, e.g. the centroid of an enumeration area. The geometric basis is a spiral whirl. Besides the regular basis, the dot clusters should not be perceived as strict geometric figures and a pseudo-random element is therefore introduced to blur the symmetry of the dot clusters. Although, this blurring is apparently random, it is repeatable. The new approach is a first step to produce dot maps automatically by providing a mathematical structure to connect the area needed for placing the dots with the number and size of the dots. The method is meant to support cartographic laypersons as well as professional cartographers in the process of map design.